1. Field of the Invention
The present invention generally relates to a substrate replacing method and a substrate processing apparatus.
2. Description of the Related Art
In an operation of manufacturing a semiconductor device, various processes (e.g., deposition, etching) are performed on a semiconductor wafer (target substrate, also simply referred to as “wafer” or “substrate”) in a vacuum atmosphere (vacuum process). Recently, a cluster-tool type multi-chamber substrate processing apparatus has begun to draw attention from the standpoint of efficiency of the vacuum process and the standpoint of preventing contamination and oxidation. The cluster-tool type multi-chamber substrate processing apparatus (hereinafter also simply referred to as multi-chamber type substrate processing apparatus or substrate processing apparatus) includes plural substrate processing chambers and a conveying chamber including a conveying apparatus. The plural substrate processing chambers are for performing a vacuum process(es) on a wafer(s). The conveying chamber, being maintained in a vacuum state, is connected to the plural substrate processing chambers. The conveying apparatus conveys the wafer into or out from the plural substrate processing chambers.
In order to convey a wafer from a wafer cassette provided at atmospheric pressure to a conveying chamber maintaining a vacuum pressure state, the multi-chamber type substrate processing apparatus has a load lock chamber provided between the wafer cassette and the conveying chamber, so that the wafer can be conveyed via the load lock chamber.
Typically, wafers are conveyed in and out between the substrate processing chamber and the load lock chamber by a conveying apparatus provided in a conveying chamber. The conveying apparatus is able to swivel inside a limited space and has two extendable conveying arms for conveying wafers to far positions. The conveying apparatus has plural combinations of conveying arms and a rotating shaft provided for a pedestal of the conveying apparatus. A conveying member (pick) is provided on each distal end of the conveying arms for mounting a wafer thereon.
In a case of conveying plural wafers by using the conveying apparatus including the conveying members and the conveying arms and performing a process on the wafers one by one, it may be necessary to determine a schedule that defines in which chamber a wafer is to be processed. For example, Japanese Laid-Open Patent Application No. 10-189687 discloses a substrate processing apparatus which assigns priority to each chamber and conveys a wafer to a chamber having highest priority.
In another example, Japanese Laid-Open Patent Application No. 11-67869 discloses a substrate processing apparatus which determines whether plural substrate processing chambers are operational and conveys a wafer only to a chamber determined to be operational.
However, the substrate processing apparatus disclosed in Japanese Laid-Open Patent Application Nos. 10-189687 and 11-67869 has the following difficulty in a case of replacing wafers in a substrate processing chamber.
The substrate processing apparatuses of Japanese Laid-Open Patent Application Nos. 10-189687 and 11-67869 can select a substrate processing chamber to which a wafer is to be conveyed beforehand. However, recently, in order to maintain the substrate processing chamber in a desired state, a cleaning process (e.g., plasma cleaning) is performed in the substrate processing chamber between a step of conveying a wafer out from the substrate processing chamber after performing a substrate processing process on the wafer and a step of conveying a subsequent unprocessed wafer into the substrate processing chamber. The subsequent unprocessed wafer cannot be conveyed into the substrate processing chamber during the cleaning process. Therefore, there is a difficulty that the conveying apparatus is required to wait in a state having the subsequent unprocessed wafer mounted on the conveying member (pick).
Particularly, because each layer of a semiconductor device is becoming thinner as design rules of semiconductor devices require finer size semiconductor devices, the times for performing a substrate processing process (e.g., deposition, etching) on wafers in the substrate processing chamber is becoming shorter. As a result, the proportion of the time for performing the cleaning process to the time for performing the substrate processing process is increasing. Therefore, in the case where the conveying apparatus is required to wait in a state having the subsequent unprocessed wafer mounted on the conveying member, the conveying apparatus is unable to perform any operations during the cleaning process. Accordingly, it is difficult to attain a satisfactory throughput of the conveying apparatus (i.e. the number of wafers that can be conveyed by the conveying apparatus per unit of time).